Replacing OM642 Turbo
IMHO it is a straight forward process, but you need to pay attention on the screws on the exhaust side. They can be tricky to be reached, because they are behind the engine and sometimes there is not a lot of space to reach those screws. I had a lengthy operation once on a ML350, because the hood compartment is just not large enough. I had to sit on the engine head and was hardly able to squeeze my hands in to reach those screws. On a CLS350CDI it was a lot smoother, because the hood is larger. Lift your hood and check if you can see the exhaust side from above once you remove the heat shield sheet metal.
Check out here at 2:12 the screws I mean:







